Hello, This is Dr. Viraj Shah, MPH, Environmental and Occupational Health expert answering your query. As your father was an exterminator all his life, he is surely exposed to pesticides and insecticides for long period of time and these chemicals are harmful. However, it is very difficult to connect an illness with the pesticides as in case of long term exposure and illness, there are less evidences that can connect the chemicals with the illness in question. Having just fever for 5 years in not a confirmatory finding to connect the fever with the use of pesticides. If your father is suffering from weight loss, loss of feelings in hands and feet, cough that does not go away or has blood in it, wounds that do not heal, problems with concentration, changes in the vision and balance, sudden mood swings etc. along with fever, then it could be due to long term side effects of the pesticides and insecticides exposure. I hope this information guides you well. Thank you for choosing HCM. Take care. Best, Dr. Viraj Shah